Presumed Parameters - Climate Change: Identification and Projections - page 64

Entirely? Whilst the laws adopted to describe the greenhouse effect come
but from calculations of physical theory. Moreover, these have been
contested (Miskolczi, 2007) and are above all unrealistic, as admitted by the
authors of the report themselves:

8.3.1: “Most intercomparison studies of the RF of GHGs are for clear-sky
and aerosol-free conditions; the introduction of clouds would greatly com-
plicate the targets of research and are usually omitted in the intercomparison
exercises [..]. It is shown that clouds can reduce the magnitude of RF due to
GHGs by about 25%”.

Where this value of 25% comes from is not specified, nor is the reason
why this reduction could not be significantly higher (why not 75% or any
other value?). Indeed, they add: “We underscore that uncertainty in RF
calculations in many GCMs is substantially higher owing both to radiative
transfer codes and meteorological data such as clouds adopted in the
simulations.”

It is also worth looking closely at the logarithmic law, assumed to apply
up to 10,000 ppm (1% of CO 2 ) . Complete saturation could occur well before,
if it has not already been reached.

Uncertainties regarding sensitivity do not result only from S = α / λ

1 1 G

, but also due to the lack of robustness regarding the
climatic reaction coefficient λ . Remember that this has an effect on the
linear approximation of the TOA flow, and is the sum of various terms.
Clouds play an essential role in this issue and according to the IPCC, “there
is a very high confidence that the uncertainties in cloud processes explain
much of the spread in modeled climate sensitivity” (AR5, Chapter 9, p.743).

the numerator

α

1

− 1

, explains
the lack of symmetry in the uncertainties. Obviously, the closer the lower
limit of

The effect of the inverse of λ on climate sensitivity,

S

= λ

G

G

is to zero - while remaining positive - the greater the relative
uncertainty is for its inverse. Hence the medium confidence , and nothing
more than this, given by the IPCC to the upper limit of climate sensitivity.
Conversely, the recent reduction by the IPCC of the lower limit of climate
sensitivity means that the stabilizing effects had previously been
underestimated. Ultimately, the feedback coefficient

λ

G

λ would not only be

G